1. Field of the Invention
This invention pertains to clutches of the type wherein the driving member is electromagnetically coupled to the driven member and both members are in rotation during use. More particularly, this invention pertains to clutches of the type described, wherein the members are hermetically isolated from each other.
2. Prior Art
One of the principal defects of conventional automotive air conditioners is the limited life of the compressor shaft seal and the loss of refrigerant which results when this seal fails. This defect has been eliminated from conventional room air conditioners by immersing the drive motor in the refrigerant and thus dispensing with the seal. In automotive air conditioners, however, compressors are driven mechanically, and shaft seals serve to confine the refrigerant. While such seals are effective when new, they do not remain so, and the resulting leakage not only renders the air conditioning system inoperative, but worse, adds to the fluorocarbon pollution of the atmosphere.
While the alternative of regular shaft seal replacement does exist, it is not viable from a consumer point of view. Equally impractical is the conversion of the conventional automotive air conditioner from mechanical to electrical hermetic drive, Since such an arrangement involves not only the initial equipment cost of an electric motor and an alternator large enough to drive it, but also the additional engine fuel needed to offset the additional losses of double energy conversion.
Hermetic shaft seals for other applications have been suggested. Thus, five patents directed to magnetically coupled pump assemblies have been issued to R. N. Zimmermann (U.S. Pat. Nos. 3,802,804; 3,545,892; 3,465,681; Re26,094; 3,205,827) wherein coupling between the impeller and drive shaft is effected by a pair of concentrically disposed permanent magnets, one rotatable with the impeller, the other rotatable with the drive shaft. A non-magnetic shield is interposed in the clearances between the magnets to isolate the impeller from the drive assembly. The synchronous drive employed in Zimmermann's pumps, while satisfactory for electric motor driven impeller pumps, is ill suited for positive displacement compressors such as those used in automotive air conditioners because they develop no starting torque to accommodate clutching, and do not damp the torque pulsations produced by these positive displacement devices.
Moreover, in some of the embodiments disclosed in Zimmermann's U.S. Pat. Nos. 3,205,827; 3,802,804; and Re26,094, the impeller shaft is supported solely by the shield. In these embodiments, shields must be thick enough not only to resist deformation resulting from pressure differences across the shield, but also from impeller loading. Worse, Zimmermann's arrangements do not effectively establish and maintain concentricity between the magnets and the shield, thus necessitating large clearances between these members and requiring magnets large enough to maintain effective coupling despite the large radial spacing.
Another magnetically coupled pump with similar deficiencies is disclosed in an article by Ian A. Hornsby in the Novemeber, 1974 issue of Processing.
U.S. Pat. No. 3,373,927 issued to Miller discloses a magnetically coupled turbine-driven centrifugal compressor in which the turbine and impeller are isolated from one another by a stationary thin wall disposed therebetween. This wall is like the shield in Zimmermann's patents in that the thin portion between the coupling magnets is totally unsupported, thus requiring excessive clearances to accommodate flexing.
Another type of hermetic shaft seal, wherein sealing is effected by means of a pressure differential, is disclosed in U.S. Pat. No. 3,392,910 issued to Tanzberger.